Thursday, June 11, 2009

With the world’s fisheries teetering on the edge of collapse, familiar items at your local sushi bar might disappear in the near future. One candidate for replacing the Hamachi, Ikura, Maguru, Tai, and Toro on the menu is the jellyfish, which seems to be doing well – too well, actually – in today’s environment.

In recent years, jellyfish outbreaks have become more frequent and more severe. These outbreaks can have lasting ecological and economic consequences. They can wreak havoc on the tourist industry by closing beaches and harming swimmers, cause power outages by blocking cooling intakes at coastal power plants, reduce commercial fish abundance via competition and predation, spread fish parasites, burst fishing nets, and contaminate catches.

A review by Anthony Richardson and his collaborators suggests that human activities such as overfishing, eutrophication, climate change, translocation, and habitat modification have dramatically increased jellyfish numbers. Their research, which was published this week in Trends in Ecology and Evolution, highlights that the structure of pelagic ecosystems can abruptly transition from one that is dominated by fish to one that is dominated by jellyfish.

Richardson and his collaborators present a potential mechanism to explain how local jellyfish aggregations can spread, displace fish, and form an alternative stable state to fish-dominated ecosystems. Jellyfish are like the opportunistic weed of the sea, giving them an edge in environments stressed by climate change, eutrophication, and overfishing. In these disturbed environments, the abundance of jellyfish relative to filter-feeding fish increases until a tipping point is reached. Under normal conditions, filter-feeding fish keep jellyfish populations in check via competition for planktonic food and (perhaps) predation on an early life-stage of the jellyfish. At the tipping point, jellyfish numbers are such that they begin to overwhelm any control of their vulnerable life-cycle stages by fish predators. At the same time, jellyfish progressively eliminate competitors and predators via their predation on fish eggs and larvae. As jellyfish abundance increases, sexual reproduction becomes more efficient, allowing them to infest new habitats where fish might have formally controlled jellyfish numbers.

Richardson and his collaborators suggest that one way to hit the brakes on what they call the “the never-ending jellyfish joyride” is to harvest more jellyfish for human consumption. Jellyfish have been eaten for more than 1000 years in China, where they are often added to salads. In Japan they are served as sushi and in Thailand they are turned into a crunchy noodle concoction. Although the taste and texture of jellyfish might not be appealing to some westerners, I for one have yet to meet a sushi that I didn’t like. Of course, jellyfish harvesting is unlikely to return systems to their fish-dominated state if the stresses that caused the ecosystem shift remain.